The initial reporting that I've seen suggests that at least two of the helicopters were taken down with small arms and MG fire--suggesting a shift in insurgent tactics rather than any deployment of new weapons systems (Iranian or otherwise). Such small arms ambushes were commonly used against Soviet helicopters in Afghanistan, and they are hardly rocket-science.

Indeed, to date, the evidence to date is that the majority of Iranian covert assistance is (ironically) still going to a US ally, SCIRI. Substantial aid is going to Sadr/Jaysh al-Mahdi, but at the moment JAM is largely going after Sunnis rather than the coalition. There is little evidence of Iranian support for Sunni insurgent groups.

Well, of course not, Anonymous. The Iranians fund the Syrians, who fund the Sunni insurgents. It'd be a bit awkward if the Iranian agents in Iraq were directly funding both "sides" of the sectarian war. They might forget which set of civilians they're supposed to be kiling at the moment.